The invention relates generally to semiconductor device fabrication and, in particular, to device structures for a bipolar junction transistor, as well as fabrication methods and design structures for a bipolar junction transistor.
Bipolar junction transistors are three-terminal electronic devices that include three semiconductor regions defining an emitter, an intrinsic base, and a collector. An NPN bipolar junction transistor includes two regions of n-type semiconductor material constituting the emitter and collector, and a region of p-type semiconductor material sandwiched between the two regions of n-type semiconductor material to constitute the intrinsic base. A PNP bipolar junction transistor includes two regions of p-type semiconductor material constituting the emitter and collector, and a region of n-type semiconductor material sandwiched between the two regions of p-type semiconductor material to constitute the base. The differing conductivity types of the emitter, base, and collector define a pair of p-n junctions, namely a collector-base junction and an emitter-base junction, across which the conductivity type changes. A voltage applied across the emitter-base junction controls the movement of charge carriers that produces charge flow between the collector and emitter.
Bipolar junction transistors may be found, among other end uses, in high-frequency and high-power applications. In particular, bipolar junction transistors may be used in radiofrequency integrated circuits, which are found in wireless communications systems, power amplifiers in mobile devices, and other varieties of high-speed end uses.
Improved device structures, fabrication methods, and design structures are needed for bipolar junction transistors.